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Abstract

Many individuals face a problem a problem characterized by compulsive drug use that:
takes place at the expense of most other activities, makes the individual unable to cease
the behavior, and makes him or her susceptible to relapse. This problem, called addiction,
has received the attention of much research in recent history. Addiction theories of
aberrant learning and reinforcement are discussed, as well as the theory of incentive
sensitization developed by Robinson and Berridge (1993). Incentive sensitization theory
suggests that sensitization of brain reward systems that attribute excessive ''wanting"
(termed incentive salience) to drugs and their related cues causes compulsive motivation
to take addictive drugs. Corticotropin-releasing factor (CRF) microinjection into the
nucleus accumbens shell enhanced the ability of a Pavlovian reward cue to trigger
increased instrumental responding for sucrose reward in a pure conditioned incentive
paradigm. Rats were first trained to lever-press for sucrose pellets, and then conditioned
to associate a Pavlovian cue (30-s clicker) with free sucrose pellets. During testing, rats
received bilateral microinjections ofintra-accumbens vehicle (saline), amphetamine
(AMPH), CRF 250, or CRF 500, and lever pressing was tested in the absence of any
contingent reinforcement. CRF potentiated the cue-elicited increase in responding in a
dose-dependent manner, indicating that stress may play a role in sensitizing neural
reward pathways leading to addiction. Findings are consistent with Berridge and
Robinson's theory of incentive sensitization.